Conveyors are often used in grading machines to transport articles through various measurement stages and to discharge the articles to sort them dependent on the measurements. Such conveyors usually include an endless chain or belt on which are mounted a plurality of article carriers or cups. A discharge mechanism is used to unload objects at certain points along the conveyor.
A common type of object that is graded and sorted by such a conveyor system is fruit. Fruit may be sorted based on criteria such as weight, shape, colour, ripeness and any other characteristic. Conveyor systems comprise devices to measure these characteristics while the fruit is being transported. The position of each fruit and its respective characteristics can be tracked so that a discharge mechanism causes items of fruit to be unloaded from the conveyor and sent to the required destination, for example towards a chute or onto another conveyor.
The applicant's own U.S. Pat. No. 7,410,044 discloses an article carrier suitable to be mounted to a conveyor and used to sort fruit in a sorting assembly. A carrier frame is pivotable between a carriage position, in which fruit may be supported on the carrier frame, and a discharge position, in which fruit may fall off the carrier frame under gravity and thereby be discharged from the article carrier. The carrier frame has contact surfaces that may be contacted by an actuator when the carrier frame is in the carriage position to cause the carrier frame to tip into the discharge position and cause a fruit on the carrier frame to be unloaded. Advantageously the carrier frame can tip in both sideways directions so that fruit can be discharged to either side.
A latch or locking member is engaged to the carrier frame and moveable between two positions in order to lock the carrier frame in position or to unlock the carrier frame and thus allow it to pivot on the article carrier.
In one version of an existing system, the actuator comprises a solenoid which, when activated, causes a pivotal trigger member to flick upwards before falling under gravity. Activation is timed so that the trigger member impacts one of the contact surfaces of the locking member, causing it to move to the unlocked position and further to transfer the impact to the carrier frame, causing the carrier frame to tip. This mechanism requires a significant amount of energy to flick the trigger upwards, which is transmitted to the latch which engages the delatching mechanism to thereupon transfer the force to the carrier frame. These series of impacts makes the conveyor system very noisy, particularly where multiple tipping actuator mechanisms are operating simultaneously. Furthermore, the impact can have a different effect on fruit of different weights. Light fruit may be caused to jump off the article carrier rather than merely tipping off. This can damage fruit and also may cause the fruit to fall or bounce somewhere other than is intended. In contrast, the force of the impact may not be sufficient to tip the carrier frame at all if it is carrying heavy fruit. Another drawback of the existing trigger mechanism is that there is a narrow window of opportunity for the trigger to be activated and to impact the carrier frame correctly. This increases the complexity in the control system and means errors in fruit discharge can easily occur where the window is missed.
The tipping trigger mechanism on MAF's Genesis conveyor system comprises a generally triangular-shaped trigger plate that has a default position laterally outside the article carriers on the conveyor. The trigger can be moved inwardly where the upper surface of the plate comes into contact with an article carrier, causing it to tip away from the trigger. The trigger is actuated by a solenoid and a spring biases the trigger back to the default position once the solenoid is de-activated. When used with light fruit, the trigger may cause the article carrier to tip violently, and therefore risks the fruit bouncing off erratically. Furthermore, the trigger is only able to accommodate the carrier tipping away from the trigger, which reduces flexibility in the design of the conveyor system. Another problem with the MAF system is that the spring mechanism to return the trigger to the default position can wear out over the course of repeated use.